1. Field of the Invention
The present invention relates to a technology for controlling a large-scale library device by using a small-scale host computer, more specifically, to a library control device for logically dividing a library device into a plurality of logical units and controlling it, and a method thereof.
2. Description of the Related Art
Recently, a library device is put to commercial use in various fields for automatically performing import/export, storage, read/write of a recording medium and the like. As such a recording medium, an optical disk, compact disk read only memory (CD-ROM), magnetic tape or so on, is utilized.
FIG. 1A is a schematic drawing of the conventional large-scale magnetic tape library. In general, a large scale magnetic tape library set (MTL) consists of frames for each function. The magnetic tape library in FIG. 1A comprises four frames, RAU, DAU 0, TAU 0, and LAU storing MT cartridges, and is controlled by the library controller 1 in the frame ACU. FIG. 1B is a schematic diagram of in the internal configuration of the subsystem of the magnetic tape library.
RAU is a frame located on the right side of the subsystem and is a frame comprising a cartridge access station (CAS) 5, accessor (ACC) 6, and a plurality of cells (CELLs) 7. CAS 5 is a special cell for importing/exporting a recording medium to the library device and is operable in the online (READY) state. ACC 6 is a robot for transporting the recording medium within the library device, and the cells 7 are slots for storing recording media.
DAU 0 is a frame comprising a direct entry exit unit (DEE) 2 and a plurality of cells 7. DEE 2 is a unit for importing/exporting a recording medium in units of frames in the offline (NOT READY) state. DEE 2, for example, by providing a rotating cell drum and a large access door 3, can perform the import/export operations of a large quantity of the recording media in a short time.
TAU 0 is a frame comprising a plurality of magnetic tape units (MTUs) 4 and a plurality of cells 7. MTU 4 is a cell for driving a recording medium for reading/writing. LAU, similar to RAU, is located on the left side and comprises CAS 5, ACC 6, and a plurality of cells 7.
ACC 6 can move arbitrarily among the frames, and transports the recording medium to and from each of CAS 5, CELLs 7, DEE 2 and MTU 4, according to an instruction from the library controller 1.
In such a conventional magnetic tape library as described above, the addresses of the CELLs 7, DEE 2, CAS 5, and MTU 4, are controlled by a combination of the frame number with the addresses within that frame. In RAU, DAU 0, TAU 0, and LAU, for example, the frame numbers 01, 02, 03, and 04 are allocated to each frame, and addresses of three bytes are utilized for each frame.
Further to this, it has been recently requested that a large-scale library device be controlled by a small-scale host computer such as a personal computer or work station. In this case, it is necessary to connect the host computer and the library device with a general purpose interface such as the small computer system interface (SCSI-2) defined in the American National Standard Institute (ANSI) X3B10 for controlling the library device as a medium changer device specified in SCSI-2. In this case, such problems are raised as described below:
(1) Generally, in SCSI, one set of a large-scale library device is defined as one logical unit. The logical unit means a unit of the control object controlled by the host computer, and the host computer can command the medium transfer in the logical unit so long as the logical unit corresponds to the medium changer device.
But, the cell addresses defined as the SCSI medium changer device are 2 bytes at most, corresponding to 216 (approximately 65,000 cells). Accordingly, a library device with a larger number of cells cannot be controlled by commands in the standard SCSI.
(2) In a conventional large-scale library device, each frame can be set into the offline state for maintenance while the subsystem is active. On the other hand, nothing can be done in SCSI to command the partial offline state for maintenance. It is necessary to set the whole library device into the offline state in this case.
(3) A set of the library device comprises CAS 5 and DEE 2 for importing/exporting a recording medium. Contrary to this, in SCSI, CAS 5 is defined as an import/export (I/E) element and DEE 2 as a storage (ST) element. Accordingly, it is impossible in SCSI to unify import/export operations of the recording medium as a function in a whole unit.
(4) It is possible to extend a large-scale library device frame by frame. But, when the library device is defined as a medium changer device in SCSI, the cell address must be revised after extension, because all the cell addresses are changed.
(5) A large-scale library device is assembled in units of frames. A plurality of frames are combined into one set of the library device, in accordance with a predetermined model. Accordingly, a frame is disposed in a different manner when the model changes. If a cell address is defined with a plurality of frames as a library device, the cell address changes relative to a model change, resulting in disabling the physical representation of the cell address from manufacture.
Conventionally, it was mandatory to write cell addresses address on completion of a model, or to write cell addresses from the viewpoint of a model to be used. Cell addresses can be determined after completion of a library device set, but it is necessary to modify addresses whenever frames are added. Accordingly, the same problem will be raised as described above in (4), in the case of address representation.
As described by items (1) to (5) above, it is extremely difficult to put the library device under the control of SCSI, in which applicable addresses are restricted, because recent large-scale library devices are equipped with much more advanced facilities than the conventional medium changer device in SCSI-2.
The object of the present invention is to provide a library control device for controlling a large-scale library device by means of such a general-use interface as SCSI and a method thereof.
In the first aspect of the present invention, the library control device comprises a memory unit and a control unit. The memory unit stores logical structure information representing the configuration of the library device divided into a plurality of logical units, each suitable for independent control. The control unit controls the operations of the library device using the logical structure information.
Each frame of the library device is, for example, regarded as one logical unit in SCSI, and the library device is divided into as many logical units as frames. Accordingly, even in such a large-scale library device with more addresses than are available using 2 bytes, each division of it is independently controllable as a medium changer device in SCSI.
In the logical structure information stored in the memory unit, 2 bytes of element addresses such as cell addresses are written for each of the logical units.
The host system issues the medium transfer commands to the medium changer device and directs the control unit to control the library device, and it is necessary to assign element addresses of an accessor, a transfer source, and a transfer destination, when the command is issued.
Accordingly, a virtual transport element is provided to logical units containing no accessor (ACC), and the element addresses are assigned. These element addresses correspond to an address of the real ACC. Thus, the medium transfer command can be issued even to logical units containing no ACCs.
Further, virtual import/export elements are provided with the function to import/export a recording medium between two logical units, so as to enable commands for recording medium transfer, and element addresses are assigned to these virtual elements.
The control unit processes the commands to different logical units in association with a check of the logical structure information, on receipt of a command for each logical unit from the host system. Based on the result of this process, the control signal is issued to control the library device.
As explained above, the logically divided library device can be controlled in a unified manner by providing virtual functional elements which do not exist in each of the library devices, in cooperation with the SCSI interface.
In the second aspect of the present invention, the library device comprises a storage unit and a control unit. The storage unit stores a plurality of recording media, and the control unit controls the library device by dividing it into a plurality of logical units, each suitable for independent control.
In the third aspect of the present invention, the control device comprises a memory unit and a control unit. The memory unit stores logical structure information representing the configuration of a control object divided into a plurality of logical units, each suitable for independent control. The control unit controls the control object using the logical structure information.
Still further, in the fourth aspect of the present invention, the host system comprises a memory unit and a command issuing unit. The memory unit stores logical structure information representing the configuration of the library device divided into a plurality of logical units each suitable for independent control. The command issuing unit issues commands to each of the plurality of logical units.